全文获取类型
收费全文 | 5756篇 |
免费 | 844篇 |
国内免费 | 642篇 |
专业分类
化学 | 1940篇 |
晶体学 | 86篇 |
力学 | 799篇 |
综合类 | 108篇 |
数学 | 1403篇 |
物理学 | 2906篇 |
出版年
2024年 | 13篇 |
2023年 | 57篇 |
2022年 | 81篇 |
2021年 | 133篇 |
2020年 | 122篇 |
2019年 | 126篇 |
2018年 | 111篇 |
2017年 | 174篇 |
2016年 | 233篇 |
2015年 | 170篇 |
2014年 | 287篇 |
2013年 | 441篇 |
2012年 | 321篇 |
2011年 | 412篇 |
2010年 | 355篇 |
2009年 | 377篇 |
2008年 | 392篇 |
2007年 | 430篇 |
2006年 | 357篇 |
2005年 | 347篇 |
2004年 | 268篇 |
2003年 | 263篇 |
2002年 | 248篇 |
2001年 | 183篇 |
2000年 | 182篇 |
1999年 | 157篇 |
1998年 | 127篇 |
1997年 | 115篇 |
1996年 | 92篇 |
1995年 | 86篇 |
1994年 | 88篇 |
1993年 | 81篇 |
1992年 | 58篇 |
1991年 | 57篇 |
1990年 | 38篇 |
1989年 | 32篇 |
1988年 | 28篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 8篇 |
1982年 | 27篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 11篇 |
1974年 | 4篇 |
排序方式: 共有7242条查询结果,搜索用时 31 毫秒
991.
992.
993.
Assume that we have iid observations on the random vector X = (X
,...,X
) following a multivariate normal distribution N
(,) where both R
and (p.d.) are unknown. Let
denote the multiple correlation coefficient between X
and (X
,...,X
). The parameter =
, called the multiple coefficient of determination, indicates the proportion of variability in X
explained by its best linear fit based on (X
,..., X
). In this paper we consider the point estimation of under the ordinary squared error loss function. The usual estimators (MLE, UMVUE) have complicated risk expressions and hence it is quite difficult to get exact decision-theoretic results. We therefore follow the asymptotic decision theoretic approach (as done by Ghosh and Sinha (1981, Ann. Statist., 9, 1334-1338)) and study Second Order Admissibility of various estimators including the usual ones. 相似文献
994.
995.
Boron-doped silicon single crystals of 207 mm diameter with various growing conditions are grown from a large amount of the melt in the cusp-magnetic Czochralski method, and the effects of growing parameters on dopant concentrations in the crystals are experimentally investigated. Equilibrium distribution coefficient of boron calculated by BPS model is 0.716. With the crystal rotation (ω) of 13 rpm and the crucible rotation of , the effective distribution coefficient (ke) is 0.751 in zero magnetic strength and increases up to 0.78 in the magnetic strength of 640 G. For , there is no significant influence of ω on ke. With , ke is almost unity. The experimental results are compared with theory. 相似文献
996.
We consider the Dirichlet problem with nonlocal coefficient given by in a bounded, smooth domain Ω⊂Rn (n?2), where Δp is the p-Laplacian, w is a weight function and the nonlinearity f(u) satisfies certain local bounds. In contrast with the hypotheses usually made, no asymptotic behavior is assumed on f. We assume that the nonlocal coefficient (q?1) is defined by a continuous and nondecreasing function satisfying a(t)>0 for t>0 and a(0)?0. A positive solution is obtained by applying the Schauder Fixed Point Theorem. The case a(t)=tγ/q (0<γ<p−1) will be considered as an example where asymptotic conditions on the nonlinearity provide the existence of a sequence of positive solutions for the problem with arbitrarily large sup norm. 相似文献
997.
T. Ishikawa S. Yamashita Y. Nakazawa A. Kawamoto M. Oguni 《Journal of Thermal Analysis and Calorimetry》2008,92(2):435-438
Thermodynamic investigation of an organic superconductor κ-(BEDT-TTF)2Ag(CN)2H2O in which the BEDT-TTF dimers are arranged in the κ-type structure in the donor layers is performed by the relaxation calorimetric
technique at low temperatures and under magnetic fields. A thermal anomaly related to the superconductive phase transition
was observed at 5 K. The existence of residual γ* in the superconductive state is about 18% of the normal state γ value, which is larger than those of κ-(BEDT-TTF)2Cu(NCS)2, and κ-(BEDT-TTF)2Cu[N(CN)2]Br salt. The lattice heat capacity reflected on the β-term in the low-temperature heat capacity was found to be affected
by the cooling rate. The disorder produced in the network structure constructed by hydrogen bond in the insulating layer is
considered to give low-energy phonon excitations reflected in the heat capacity. 相似文献
998.
999.
In a traditional quartz crystal microbalance (QCM), an AT-cut (cut angle φ = 35.25° in yxl orientation) quartz wafer is employed because it has low frequency–temperature coefficients (dF/dT) at room temperature region. But when a QCM is in contact with a liquid phase, its frequency is also related to the properties of the liquid, which are temperature dependent. The value of dF/dT is about 20 Hz/°C for a 9 MHz AT-cut QCM with one side facing water. In this work, a group of QCMs in new cut angles were prepared. The influence of the cut angle on the frequency–temperature characteristic, response sensitivities to surface mass loading and viscodensity of liquid were investigated. An intrinsically temperature-compensated QCM sensor that possesses low dF/dT values in aqueous solution was reported. When a 9 MHz QCM with φ = 35.65° was contacted with water with one side, its dF/dT value is close to zero at ca. 25 °C and its averaged value of |dF/dT| is only 0.6 Hz/°C in the temperature range of 23–27 °C. The frequency responses to surface mass loading and viscodensity of liquid phase are very close among the QCMs with the cut angles in the range of 35.15–35.7°. The intrinsically temperature-compensated QCM was applied to investigate the alternate adsorption processes of cationic polyelectrolyte and silica nanoparticle. 相似文献
1000.